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Counsel needed for OT for 4p1l line stage

173.200.6.182

Posted on September 5, 2014 at 14:11:35
Posts: 3040
Location: Atlanta
Joined: December 15, 2003
Kevin,

I have been following Moglia's schematic for a 4p1l line stage. He is using the LUNDAHL LL1660.

I see you are using the LL1692A. You are too familiar with my limitations when it comes to transformers and how to decide which one to use. I need your guidance.

Moglia has found the tube sounds best run with 40 mA of current. I guess one can choose from various 1660s based on power. I would not know what to ask for!

Seeing that you are using the LL1692A makes me think I should pay attention to what you have chosen.

Would this transformer survive the same amount of power as the model of LL1660 used by Moglia? (hoping you know which one or you can guess which one)

What is the essential difference between the two? I would guess gain? Could I get around 6 dB of gain with either one of these? This line stage will only be used below 500 Hz so low frequency performance would be more important than going into the stratosphere.

Any help would be appreciated.

I am curious why you did not use the LL1683 in your prototype? I plan on using one in mine though I wonder if one would be sufficient for two channels? Your opinion please.

Take care,

 

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RE: Counsel needed for OT for 4p1l line stage, posted on September 5, 2014 at 16:27:34
KevinC
Manufacturer

Posts: 2984
Location: NC
Joined: April 19, 2001
For an application below 500Hz there's no real basis to choose between the LL1660 and the LL1692A. I use the LL1692A instead of the LL1660, because the somewhat lower impedance of the LL1692A pushes any circuit resonances (peaks in frequency response) further above 20kHz compared to the LL1660. I've not measured the higher than 20KHz frequency response yet, so this is only theoretical, but it has worked for other lower Rp tubes in the past.

Kevin Carter
K&K Audio
www.kandkaudio.com

 

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